Introduction

Although the broadband data market segment has been
rather anemic for the past couple decades, declining
average revenue per user has caused carriers to look at
wireless broadband data as a means to drive revenue
growth. While growth of low-bandwidth applications
such as downloading ring tones and SMS are
experiencing sharp growth, the growth of broadband
data applications such as email and downloading/
uploading files with a laptop computer or PDA has been
slow. Primary inhibitors of portable broadband services
have included service price, slow data speed and spotty
coverage.
Early Wide Area Network Technologies (WAN) such as
General Packet Radio Service (GPRS) offered average
throughput speeds of 10 Kbps, which was far too slow
for user satisfaction. In 2003, carriers began deploying
services such as Enhanced Data rates for Global
Evolution (EDGE), which delivers average speeds of
100-130 Kbps and bursty traffic up to 200 Kbps. Code
Division Multiple Access (CDMA) technologies such as
1xEvDO provide average speeds of ~300–400 Kbps
with bursts up to 700 Kbps; EVDV boosts these speeds
even higher.[5]
Recent research from In-Stat/MDR* (4/04)[5] indicates
that laptop computers are becoming the access devices
of choice for broadband wireless data. Personal
productivity applications such as email, address books,
calendars, and internet browsers, are among the top
applications used.
While many service providers and operators may be
somewhat familiar with the previously mentioned 2.5G
services, they are now hearing about newer 3G
technologies such as UMTS and HSDPA, and other
technologies such as WiMAX (IEEE 802.16e), which
offer substantial improvements in data rate and spectral
efficiency. This paper focuses on the technical
differences between these technologies by comparing
the differences between the modulation techniques
used in CDMA and OFDMA.



Technology Overview

WCDMA

Wideband Code Division Multiple Access uses Direct
Sequence Spread Spectrum (DSSS) to spread the
signal over a 5 MHz spectrum. It is based on 3GPP
Release 99 and provides data rates of 384 Kbps for
wide area coverage and up to 2 Mbps for hot-spot
areas. In addition to the use of orthogonal spreading
codes, it uses Quadrature Phase Shift Keying (QPSK)
for its modulation.

High Speed Downlink Packet Access
(HSDPA) Overview

WCDMA 3GPP Release 5 extends the WCDMA
specification with High Speed Downlink Packet Access
(HSDPA). HSDPA adds a new transport channel, the
high-speed downlink shared channel (HS-DSCH),
which is optimized for shared data. It also provides
higher-order modulation (Quadrature Amplitude
Modulation or QAM), short transmission time interval
(TTI), fast link adaptation, fast scheduling, and fast
hybrid automatic-repeat-request (ARQ).

WiMAX (IEEE 802.16e)

The portable version of WiMAX, IEEE 802.16e utilizes
Orthogonal Frequency Division Multiplexing Access
(OFDM/OFDMA) where the spectrum is divided into
many sub-carriers. Each sub-carrier then uses QPSK or
QAM for modulation. For more on the basics of OFDM,
refer to Orthogonal Frequency Division Multiplexing.